Is the book you're looking for The Mischief of the Mistletoe?
In their "Click to Read It Now" box under that book, Amazon is showing "Tell the Publisher", which is their sign that the book isn't available for pre-order as an eBook.
I'd write to the publisher to inquire when an epub version of the eBook will be available.
The Dutton/Gotham Fall 2010 catalog says on page 19: "Also available as an e-book". As always, it doesn't say when, but usually that means at about the same time.
It's still a month and a half away, and pre-orders on e-books are squirrely. Chances are good that even if it were available for pre-order, the pre-order price would be outrageous.
So my advice is to have patience and see what happens when October 28 rolls around.